The invention refers to a gas-tight, maintenance-free high capacity lead battery or accumulator according to the characterizing clause of claim 1.
A gas-tight seal and maintenance-free operation are rendered possible by the use of an electrolyte containing sulfuric acid in the form of a thixotrope where an evaporation of fluid or a gassing is essentially excluded. High capacity accumulators equipped in such way shall be those in which because of the bigger or higher construction as a function of the charging status such quantities of free non-solid or gaseous electrolyte evade from the gel or the active mass or the separators respectively that they can no longer be disregarded. A greater problem is especially the assembly of such an accumulator in a horizontal position which, because of the easier positioning, charging and operation and a space-saving stowage, is the preferred position for larger arrangements with a variety of accumulators positioned side-by-side or on top of each other in one rack. In such case the free sulfuric acid can reach the pressure control valve which is always present for safety reasons, and thus can escape to the outside.
During a discharge the volume of the electrolyte decreases and the volume of the active masses of the electrode plates increases, during charging this is the other way round. In this case gas additionally emerges in the pores of the electrode plates which displaces the electrolyte present there. The electrolyte volume is partially reversibly absorbed by the gel structure. As a result a quantity of liquid electrolyte which cannot be ignored occurs above the plate group.
For this reason the German application DE 37 27 763 C1, which corresponds to U.S. Pat. No. 4,894,300, provides a partition for a horizontal arrangement of the accumulator which closes the space between electrode plates and cover in a lower section, which also covers the charging hole. The space is preferably filled with a sealing cellular material which is injected. The term lower section here refers to the horizontal arrangement. The free sulfuric acid electrolyte can then only occur in the remaining upper free space between electrode plates and case cover. The pressure control valve which is required nevertheless is positioned at a side wall of the accumulator in such way that in horizontal position it faces upwards.
The arrangement described there has the disadvantage that such an accumulator can only be operated in the horizontal position, that even in such a specific horizontal position in which the pressure control valve is positioned in the upper sidewall has to be chosen, that the free space still available adjacent the control valve is relatively small so that there can be frequent excess pressure reactions, i.e. discharging via the pressure control valve, which might impair availability. A combination of such a horizontal battery with another vertical battery in one common rack is complicated, time-consuming and requires more space. If only one horizontal position is possible where, for example, all positive terminals are positioned above the negative terminals, a longer diagonal connection with the negative terminals of the adjacent battery is required. It is further undesirable to provide two different battery types for a horizontal arrangement with higher expenses for manufacture, storage and distribution where in a first type the negative terminals and in a second type the positive terminals is positioned uppermost when the accumulator is in horizontal position.
DE 40 32 990 A1 suggests to lead the gas outlet from one side below the cover to the centrally fitted valve so that the electrolyte in the horizontal position of the accumulator can rise via the centre of the cell. The accumulators can only be displaced to a specific side which is disadvantageous and can lead to installation errors.
JP- OS 87-157673 describes a lead accumulator using a separator with glass fiber as its main component. This separator has average openings of between 30 and 50 .mu.m. The quantity of the water and the pressure are related to the average diameter of the openings. The absorbing power for fluids in the negative electrode plate shall thus become higher than for the separator. The distribution of electrolyte in the accumulator shall thus become more even, the storage capacity shall thus be improved and the drop in capacity be suppressed. This arrangement is only suitable for influencing small plate areas. The issue of a horizontal arrangement of large-scale batteries of between about 200 and 1200 ampere-hours is not discussed in this reference.
Besides zigzag-shaped electrode grids JP OS 87 115658 suggests thick separators of hydrophilic synthetic material or glass fiber with an average thickness of 1 .mu.m or more for the largest proportion of the separator sections, whereas correspondingly thinner glass fibers are provided in the remaining section. Additionally, electrolyte holding devices, for example of hydrophilic porous synthetic material, are suggested which contain fine silicium powder having a greater aptitude to hold electrolyte than a separator. By these measures the use of very expensive separators shall be avoided despite the even distribution of electrolyte. JP- OS 87-115659 too suggests the combination of thick separators of hydrophilic synthetic material or glass fibers with thinner separators for other groups of electrode plates, it further suggests an additional electrolyte holding body of hydrophilic, porous synthetic material with fine silicium powder and a higher holding capacity compared to the separator. Here too the problematic nature of accumulators in horizontal position is not discussed.
The invention is based on the problem of designing a gas-tight, maintenance-free high capacity lead accumulator according to the characterizing clause of claim 1 in such way that the accumulator can be operated in a horizontal as well as in an upright position avoiding two different accumulator versions where the positive or the negative terminal can be positioned one above the other.
This problem is solved in accordance with the invention by the characterizing features of claim 1. Further embodiments of the invention are protected by the subclaims.
In the free spaces of the accumulator the invention provides layers of fibrous web which absorb free, especially liquid electrolyte under specific charging conditions and which again release it to the gelous electrolyte or the active masses of the electrode plates respectively under different charging conditions.
Elastic, highly porous material, preferably with a porosity of between 90 and 99% is used as fibrous web. To adapt this fibrous web to the requirements of the accumulator, this fibrous web is preferably pressed together to a certain extent.
The fibrous material is suitably positioned at the lateral edges, at the bottom and above the edges or above the terminal bars of the electrode plates. Besides glass fiber, polyester and polyethylene can in particular be used as material.
In practice the following areas of a maintenance-free accumulator are responsible for the binding of electrolyte:
a) The pores in the positive and negative electrode plates, from which the cyclic formation and binding of the electrolyte originates. PA1 b) A fine pored gel structure between electrode plates and separators. It holds the electrolyte very tight. Apart from that electrolyte can flow into further pore systems through existing cracks within the gel structure. These cracks also transport the gas bubbles. PA1 c) The pores of the separator; the gel particles can hardly penetrate into these pores, the electrolyte is thereby very tightly held in the pores of the separator. PA1 d) The pores of the fibrous web provided according to the invention are mostly filled to a large extent between the lateral edges and the side wall as well as possibly at the bottom of the case. PA1 e) Excess electrolytic fluid present flows into the pores of the fibrous web slightly pressed together which is positioned above the electrode plates. These mainly absorb the changing free electrolytic volume of the accumulator. Here the lower sections are filled first depending on whether the battery is arranged in vertical or horizontal position. In accordance with the ability to rise within the capillaries of the fibrous web the upper sections of the fibrous web are then eventually filled too so that there remains hardly any free electrolytic fluid in the free space near the pressure control valve.